Bibcode
Lázaro, C.; Martínez-Pais, I. G.; Arévalo, M. J.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 351, Issue 2, pp. 707-720.
Advertised on:
6
2004
Citations
16
Refereed citations
15
Description
We present the results of an analysis of our infrared light curves of
the Algol-type binary AI Draconis in the J, H and K bands, and of
published light curves in the B, V and Strömgren uvby bands,
together with spectra obtained by us. The analysis of the light curves
was carried out using a code based on ATLAS model atmospheres and Roche
geometry.
The small contribution of the secondary cool component to the total
light of the system in the visible, producing light curves with very
shallow secondary eclipses, makes the stellar and orbital parameters
derived from light-curve analysis in the visible spectral range
uncertain. The larger contribution of the secondary star to the infrared
fluxes makes this range particularly well suited to the derivation of
precise orbital and stellar parameters in binaries of Algol type. From
the simultaneous solution of the infrared JHK light curves, we derive
the following absolute orbital and stellar parameters for the two
components: = 10160 +/- 160 K,
Req,1= 2.12 +/- 0.04 Rsolar,
log()1= 4.23; = 5586 +/-
110 K, Req,2= 2.36 +/- 0.04 Rsolar,
log()2= 3.76; M1= 2.86 +/- 0.09
Msolar, q=M2/M1= 0.44 +/- 0.03; a= 7.62
+/- 0.09 Rsolar, i= 76.53°+/- 0.3°, e~= 0.0. Here,
and log() indicate average surface
values, Req is the equivalent radius of the deformed star and
a is the orbital size.
In our light-curve solutions, the secondary star of AI Dra fills its
Roche lobe (as also indicated by the spectroscopy), thus discounting
claims, based on UBV light curves, that both components of the binary
are located within their Roche lobes. The visible and infrared
photometry show no evidence of any significant infrared excess in the
system, and the distance of AI Dra is estimated as d= 169 +/- 17 pc.
Based on the spectra of AI Dra and template stars in the ranges
8210-9060, 6250-7130 and 4040-4920 Å, we classify the stellar
components of AI Dra and find that the most probable spectral types are
A0V (or perhaps A1V) for the primary and F9.5V for the secondary
(although it could reach as far as G4V), respectively. From our
spectroscopic observations, the spectral evolution of AI Dra with
orbital phase is also presented. Furthermore, we obtain the projected
rotational velocity of the secondary, whose value turns out to be
compatible with the star filling its Roche lobe.